Method of separating fatty acids



Patented Nov. 20, 1951 METHOD OF SEPARATINC FATTY ACIDS Latimer D. Myers, Cincinnati, Ohio, assignor to Emery Industries, Inc.

poration of Ohio Cincinnati, Ohio, a cor- No Drawing. Application August 24, 1945, Serial No. 612,545

1 This invention relates to a process of obtaining fatty acid fractions which differ from one another in melting point and in degree of unsaturation.

Fatty acids of the type to which this invention is directed occur combined with glycerine in the fats and oils of animal, vegetable and marine origin. These esters are usually termed fatty triglycerides or mixed triglycerides, both because two or more chemically different fats are almost always in admixture in any particular natural product, and because two or more different fatty acid radicals may be, and usually are, attached to a single glycerine molecule. In view of this latter condition, which obtains almost universally the separation of the triglycerides one from another, accomplishes, and can accomplish, no more than a rough or approximate fractionation. If, on the other hand, the fats are decomposed by the destruction of the esters and the removal of the glycerine, then the fatty components may be separated with far greater discrimination.

Natural occurring glycerides vary greatly in the composition of the fatty acid radicals. Thus, tallow contains approximately 45% saturated acids, and 55% of liquid acids, mostly oleic acid; linseed oil contains approximately 10% saturated acids, 20% oleic acid, 20% linoleic acid and 50% linolenic acid; soyabean oil contains approximately 13% saturated acids, 30% oleic acid, 52% linoleic acid and 5% linolenic acid.

The separation of solid and liquid fatty acids has long been accomplished in the fatty acid industry by splitting various grades of animal fats, then cold pressing out the liquid fraction to provide commercial stearic acid (the eutectic mixture of stearic and palimitic acids) and commercial red oil (oleic acid). An improved method of obtaining a low iodine value commercial stearic acid and a low titre oleic acid is disclosed in United States Patent No. 2,293,676 to Latimer D. Myers and Victor J. Muckerheide, issued August 18, 1942, for "Method of Separating Fatty Acids. The process of the present invention is alternative to these processes and possesses the advantage that it can be operated with appreciably less refrigeration.

The obtaining of special liquid fatty acid fractions, different from those found in nature or different from the starting raw material, may be desirable for a multitude of industrial purposes. For instance, drying oils and semi-drying oils contain non-drying constituents, namely saturated fatty acids and monoethylenic fatty acids. The saturated fatty acids contribute to an undesirably soft film, and the monoethylenic acids 25 Claims. (Cl. 260-419) cause tackiness. Thus it is advantageous to remove both of these constituents in whole or in part, if possible.

A number of methods of separating liquid fatty acids has been proposed; 1. e. distillation, solvent separation of acids. solvent separation of glycerides and solvent separation of soaps.

All of these methods are unsatisfactory in some respect. Distillation of fatty acids does not produce appreciable separation of acids of the same chain length. The separation of soaps requires low temperatures and requires decomposition of the soaps which is costly. Solvent separation of glycerides is not particularly satisfactory. because the fatty acid radicals are more or less randomly distributed, making it necessary to remove large amounts of glycerides to obtain substantial improvements in the oil. Solvent separation of the It is the purpose of this invention to provide a method and a process by which solid fatty acids may be obtained separate from liquid fatty acids and/or by which fractions of liquid fatty acids of different degrees of unsaturation may be produced.

This invention is predicated upon the discovery and determination'that the amides of fatty acids dissolve at slightly elevated temperatures in a multiplicity of readily available commercial solvents, that on cooling. the amides precipitate selectively from these solvents at temperatures relativel high in comparison with the temperatures to which the acids precipitate from like solvents, that the precipitates are readily @terable from the slurry and that the filter cake may be easily washed. The invention also involves the determination that amides may be efficiently and economically produced, either directly from the fatty glycerides or from the fatty acids themselves after splitting and the separation of the glycerine, and that the fatty amides may be completely and economically converted to the corresponding fatty acids after fractionation.

The invention as a whole, therefore, involves a multiplicity of steps, namely:

1. Preparing mixed fatty amides from the commercial mixed triglycerides or fatty acids.

2. Dissolving the amides in a solvent.

3. Chilling the solvent or otherwise lowering the solvent capacity to create a slurry containing a precipitate of the more saturated amides.

. 3 4. Filtering the precipitate from the slurry,

accompanied by washing the precipitateif sharp fractionation is required.

5. Removing the solvent from the amides remining in solution.

6. Converting the amides to the corresponding fatty acids.

There may, of course, be instances in which the last step is not used; for instance, where the ultimate products desired are the amides themselves. the corresponding nitriles, the amines, or amide addition products. Insofar as the method and process herein disclosed is utilized to obtain these nitrogen containing materials as end products, this method or process may be said to be one of separating fatty amides, or of obtaining fractions of fatty amides of different degrees of unsaturation.

The amides may be obtained from either the fatty glycerides or the fatty acids by heating them under pressure, ammonia gas being passed continuously through a reaction zone over a period of time. In general, the process operates more rapidly on free fatty acids than on the glycerides. The choice between treating the glycerides directly with the ammonia and splitting the glycerides then treating the fatty acids with the ammonia, is a question both of economics and of the integration of the amide-forming operation with other manufacturing processes conducted in the same plant. The availability of equipment may also be a determining factor in the selection between the two alternative methods of preparing the amide. The amides are then dissolved in a solvent which may be polar, semipolar or non-polar. The fatty amides are less soluble in the solvents than their corresponding fatty acids, in the sense that the amides precipitate from the solvent at relatively higher temperatures. In most instances, therefore, it is necessary to warm the amides and solvent in order to constitute the solution.

For the separation of saturated solid fatty amides from liquid fatty amides, any type of solvent may be used which has the capacity to dissolve the amides, provided of course the solvent is chemically stable and does not solidify within the operating range. Among such solvents are aliphatic alcohols, methyl through amyl, the acetates, methyl through isobutyl acetate, acetone, methyl ethyl ketone. ethylene dichloride and petroleum hydrocarbons.

For the separation of the unsaturated liquid amides, however. the semi-polar and polar solvents are very much preferred, for instance, methyl alcohol, isopropyl acetate and the like. This is because the petroleum hydrocarbon type of solvent does not precipitate these liquid unsaturated amides with the selectivity or degree of fractionation which can be accomplished by.

the use of the types of solvents recommended.

The liquids which dissolve the fatty amides precipitate the amides on chilling with different degrees of selectivity, but most of the commonly available solvents, including those listed, precipitate the amides from the solution with a very substantial selectivity. Generally speaking, the percentage of amides in the solvent should not exceed 20 to 30% by weight in order to secure this desired selectivity or fractionation upon precipitation and in order to provide a filterable slurry on chilling.

Preferably the fatty amides are treated by a continuous process in which they are heated sufiiciently to render them fluid; the solvent and amides are pumped, each at a metered rate, and comingied, the amides dissolving in the solvent: the flowing stream of solvent solution is chilled progressively after which the precipitate is separated from the slurry in a continuous filter. The solvent is then distilled from the filter cake and from the amides remaining in solution, after which it may be reused.

After the 20 to 30% solvent solution has been constituted, its solvent capacity is decreased to precipitate certain fatty amides present in the solution and to constitute a filterable slurry. While this decrease in the solvent power of the solvent can be diminished by dilution of the solvent with a material which is not a solvent f or the fatty amides, by diluting an alcohol solution with water, for instance, the preferable way of precipitating the desired slurry is to chill the amide solution.

With a solution of the type and strength specified, a substantial precipitation of unsaturated fatty acids takes place in the temperature range of to 20 C. This range corresponds with temperatures of from 104 to 68 F. Thus, under most conditions, in most climates, and with most solvents, the amides must be warmed slightly to be dissolved and precipitate to some degree on cooling to normal room temperature.

Obviously, in many climates the separation could be very easily accomplished by a batch process operated on a 24-hour cycle to utilize the heat of the middle of the day to dissolve the amides in solvent and the over-night chill to effeet the precipitation of solid amides.

If the separation of liquid from liquid fatty acids is desired, the temperature is reduced substantially lower, for instance from 5 to 0 C. The precipitate is then separated from the slurry by centrifuging or filtering. The process is particularly intended and adapted to be practiced as a continuous process employing a vacuum filter, because the precipitate is very readily filterable and does not require the careful and accurate control of composition and conditions which are necessary in order to secure and maintain the requisite filterabillty characteristic when fatty glycerides or fatty acids are being processed. The filter cake may be washed during or after the filtering operation, as is well known in the art of solvent separation.

Whenever desirable, the chilling and filtering can be carried out in a succession of steps. That is, the temperature can be lowered to 25 C. and one fraction of fatty amides filtered from the solution as a precipitate, then the temperature can be lowered to 5 C. and another fraction of amide filtered from the solution as a precipitate. Any number of fractions of amides may be segregated, but generally speaking, the important types of separation are two in number, namely, separation of solid saturated fatty acids from liquid unsaturated fatty acids, and separation of monoethylenic fatty acids from polyethylenic fatty acids.

Example I 400 grams of distilled animal fatty acids were heated in an autoclave with ammonia at 125 pounds pressure and 185-190 C. Ammonia was passed through the reaction at the rate liters per hour for eight hours. The free fatty acid content at this time was 2.3 percent. 100 parts of this amide was dissolved in 400 parts of percent methanol. The solution was allowed to cool to 25 C. at which point the precipitate was filtered and washed with parts of 90% methanol.

tent 101.2% calculated as oleic acid.

' The residue above was split in the same manner to yield oleic acid of titre 21.0 C. and iodine value of 85.0.

Example II 200 parts by weight of linseed oil was mixed with 200 parts of 28% ammonium hydroxide in an autoclave and gaseous ammonia admitted to 125 pounds pressure. The reaction was heated at 10-190 C. for six hours and then the excess ammonia allowed to escape. The aqueous layer was withdrawn and concentrated to recover the glycerine. Ammonia was passed through the fatty residue at 125 pounds presure and 180- 200C. for six hours.

at this time was 1.8% .100 parts of the above amide was dissolved in 400 parts of acetone. The solution was cooled The free fatty acid content with agitation to C. Filtration and washing at this temperature gave 45.9 percent of amides of iodine value 140.8 after removal of the solvent. Removal of the solvent from the residue left 53.9% of amides of iodine value 207.9.

Example III 100 parts by weight of animal fatty amides prepared as in Example I were dissolved in 400 parts of ethylene dichloride and separations taken at 35 C. and 25 C. The following results were obtained: I

Per (Jen Iodine Separate." Value These results show a sharp separation of saturated and unsaturated acids,

Ezampl e IV 480 grams of linseed acid were converted to amide by heating to 180-190 C. for seven hours at 125 pounds pressure of ammonia, allowing ammonia to escape at a rate of 1.5 l. per min. The free fatty acid content was 3.3%.

100' parts by weight of amides were dissolved in 400 parts of 90% methanol and cooled slowly to C. The precipitate after washing and removing the solvent had an iodine value of 145.6 and amounted to 46.0%. Removal of the solvent from the filtrate left 54.0% of amides of iodine value 209.6. After splitting these amides, as in Example I, acids of iodine value 212.8 were obtained.

An alkyd resin made from these acids dried in two hours as compared to 8.5 hours for alkyd resin prepared from the original acids.

Example V 100 parts by weight of soyabean amides prepared as in Example IV were dissolved in 400 parts isopropylacetate and cooled to 40 C. After filtering and washing. the solvent was removed from each part. The precipitated amides had an iodine value of 105.3; the amides remaining in solution and recovered by evaporating the solvent had an iodine value of 161.0.

While this process has been described in relatlon to an apparatus utilizing a chiller and filter, it will be obvious to those skilled in the art that alternatively the solvent power of the solution may be diminished by diluting instead of chilling, and that the precipitate may be separated from the solution centrifugally instead of by means of a filter. However, with the equipment at present available, the process can be carried out most expedi'ently and economically by the use of the preferred equipment.

Having described my invention, I claim:

1. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising preparing fatty amides, dissolving the fatty amides in a solvent, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty amides remaining in solution, separating the fatty amides from the solvent, and converting the fatty amides into corresponding fatty acids.

2. The method of fractionating fatty amides. which comprises dissolving the fatty amides in a solvent, lowering the temperature of the solvent to precipitate part of the fatty amides, and separating the precipitated fatty amides by filtration.

3. The method of separating fatty amides, which comprises dissolving the fatty amides in a solvent at a temperature of above 70 F., then cooling the solvent to precipitate part of the fatty amides dissolved in the solvent, and removing the precipitated fatty amides from thesolvent.

4. A method of separating oleic acid from linoleic acid, said method comprising preparing the amides of oleic and linoleic acids in admixture, dissolving the amides in a solvent and lowering the temperature of the solvent to substantially 5 C. to minus 10 C. to precipitate the monoethylic fatty amides, filtering the precipitate from the solution, evaporating the solvent from the polyethylic fatty amides remaining in solution, and converting said fatty amides to corresponding fatty acids.

5. A method of obtaining commercial stearic fatty acid of low iodine value and. a liquid red oil fraction of low titre, said method comprising converting animal fats to fatty amides, dissolving said fatty amides in a solvent at a temperature above room temperature, lowering the temperature of the solution to precipitate substantially all of the saturated fatty bodies, filtering said precipitate from the solution and lowering the temperature of the solution to precipitate the unsaturated fatty bodies from the solution, and removing them by filtration and reconverting said fatty amides to the corresponding fatty acids.

6. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising treating fatty glycerides with ammonia to produce fatty amides, dissolving the fatty amides in a solvent, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fattyamides from the fatty acids remaining in solution, separating the fatty amides from the solvent, and converting the fatty amides into corresponding fatty acids.

7. A method of obtaining commercial stearic fatty acid of low iodine value and a liquid red oil fraction of low titre, said method comprising con- 7 verting animal fats to fatty amides, by treating them with ammonia, dissolving said fatty amides in a solvent at a temperature above room temperature, lowering the temperature of the solution to precipitate substantially all of the saturated fatty bodies, filtering said precipitate from the solution and lowering the temperature of the solution to precipitate the unsaturated fatty bodies from the solution, and removing them by filtration and reconverting said fatty amides to the corresponding fatty acids.

8. The method of obtaining batches of mixed fatty acids of different melting points. said method comprising treating fatty glycerides with ammonia to produce fatty amides, dissolving the fatty amides in a solvent, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty acids remaining in solution, separating the fatty amides from the solvent, converting the fatty amides into corresponding fatty acids, and hydrolyzing the amides by heating them under pressure with water to release the ammonia and removing the ammonia so released and reusing it to prepare additional fatty amides. 9. A method of obtaining commercial stearic fatty acid of low iodine value and a liquid red oil fraction of low titre, said method comprising converting animal fats to fatty amides, by treating them with ammonia, dissolving said fatty amides in a solvent at a temperature above room temperature, lowering the temperature of the solution to precipitate substantially all of the saturated fatty bodies, filtering said precipitate from the solution and lowering the temperature of the solution to precipitate the unsaturated fatty bodies from the solution, and removing them by filtration, reconverting said fatty amides to the corresponding fatty acids, and hydrolyzing the amides by heating them under pressure with water to release the ammonia and removing the ammonia so released and reusing it to prepare additional fatty amides.

10. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising treating fatty bodies with ammonia to produce fatty amides, dissolving the fatty amides in a solvent, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty acids remaining in solution, separating the fatty amides from the solvent, converting the fatty amides into corresponding fatty acids, and hydrolyzing the amides by heating them under pressure with water to release the ammonia and removing the ammonia so released and reusing it to prepare additional fatty amides.

11. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising preparing fatty amides, dissolving the fatty amides in a solvent selected from" the group consisting of polar and semi-polar solvents. lowering the temperature of the solvent to-precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty acids remaining in solution, separating the fatty amides from the solvent, and converting the fatty amides into corresponding fatty acids.

12. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising preparing fatty amides, dissolving the fatty amides in a polar solvent, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty acids remaining 8 in solution, separating the fatty amides from the solvent, and converting the fatty amides into corresponding fatty acids. 7

13. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising preparing fatty amides, dissolving the fatty amides in a semi-polar solvent, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty acids remaining in solution, separating the fatty amides from the solvent. and converting the fatty amides into corresponding fatty acids.

14. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising preparing fatty amides, dissolving the fatty amides in methanol, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty acids remaining in solution, separating the fatty amides from the solvent, and converting the fatty amides into corresponding fatty acids.

15. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising preparing fatty amides, dissolving the fatty amides in acetone, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty acids remaining in solution, separating the fatty amides from the solvent, and converting the fatty amides into corresponding fatty acids.

16. The method of obtaining batches of mixed fatty acids of different melting points, said method comprising preparing fatty amides, dissolving the fatty amides in isopropyi acetate, lowering the temperature of the solvent to precipitate part of the fatty amides dissolved, separating the precipitated fatty amides from the fatty acids remaining in solution, separating the fatty amides from the solvent, and converting the fatty amides into corresponding fatty acids.

17. The method of obtaining differentiated fatty acids which are characterized by different degrees of unsaturation from mixed fatty bodies which contain carbon chains which are saturated to different degrees, said method comprising synthesizing the amides of the fatty bodies which correspond in length of carbon chains to the fatty acids ultimately desired, dissolving said fatty fatty amides in solvent, precipitating more saturated fatty amides from the solvent by decrease of the temperature of the solution, removing the fatty amides so precipitated from the solution, separating the fatty amides remaining in solution from the solvent and hydrolyzing said fatty amides to their corresponding fatty acids.

18. The method of obtaining differentiated fatty acids which are characterizedby different degrees of unsaturation from mixed fatty bodies which contain carbon chains which are saturated to different degrees, said method comprising synthesizing the amides of the fatty bodies which correspond in length of carbon chains to the fatty acids ultimately desired, disolving said fatty amides in a polar solvent, precipitating more saturated fatty amides from the solvent by decrease of the temperature of the solution, removing the fatty amldes so precipitated from the solution, separating the fatty amides remaining in solution from the solvent and hydrolyzing said fatty amides to their corresponding fatty acids.

19. The method of obtaining differentiated fatty acids which are characterized by different degrees of unsaturation from mixed fatty bodies which contain carbon chains which are saturated to different degrees, said method comprising synthesizing the amides ofthe fatty bodies which correspond in length of carbon chains to the fatty acids ultimately desired, dissolving said fatty amides in solvent which is more polar than a petroleum solvent, precipitating more saturated fatty amides from the solvent by decrease of the temperature of the solution, removing the fatty amides so precipitated from the solution, separating the fatty amides remaining in solution from the solvent and hydrolyzing said fatty amides to their corresponding fatty acids.

20. The method of obtaining differentiated fatty acids which are characterized by diiferent degrees of unsaturation from mixed fatty bodies which contain carbon chains which are saturated to different degrees, said method comprising synthesizing the amides of the fatty bodies which correspond ni length of carbon chains to the fatty acids ultimately desired, dissolving said fatty amides in solvent to provide a solution containing substantially 20-30% amides by weight, precipitating more saturated fatty amides from the solvent by decrease of the temperature of the solution, removing the fatty amides so precipitated from the solution, sepaarting the fatty amides remaining in solution from the solvent and hydrolyzing said fatty amides to their corresponding fatty acids.

21. The method of separating long-chain fatty amides which are characterized by differentdegrees of unsaturation from a mixture of such fatty amides, said method comprising dissolving the mixed fatty amides in a solvent, lowering the temperature of the solvent to precipitate the more saturated fatty amides, separating the precipitate from the solvent and separating the solvent from the fatty amides remaining in solution.

22. The method of separating aliphatic longchaln fatty amides which are characterized by different degrees of unsaturation from a mixture of such fatty amides, said method comprising dissolving the mixed fatty amides in a solvent which is more polar than a petroleum solvent, lowering the temperature of the solvent to precipitate the more saturated fatty amides, separating the precipitate from the solvent and separating the solvent from the fatty amides remaining in solution.

23. The method of separating aliphatic long- 10 vide a. solution containing substantially 20-30% amides by weight, lowering the temperature of the solvent to precipitate the more saturated fatty amides, separating the precipitate from the solvent and separating the solvent from the fatty amides remaining in solution.

24. The method of obtaining a mixture of linoleic and linolenic acids from a mixture of fatty bodies which contains carbon chains of eighteen-carbon chain length, some poly-unsaturated and other unsaturated to a lesser degree, said method comprising synthesizing amides of eighteen-carbon chain length from the fatty bodies, dissolving said amides in solvent, lowering the temperature of the solvent to precipitate the amides which are not polyunsaturated, separating such amides from the solution, separating the fatty amides remaining in solution from the solvent and hydrolyzing said fatty amides to linoleic and linolenic acids.

25. The method of obtaining a mixture of linoleic and linolenic acids from a mixture of fatty bodies which contains carbon chains of chain fatty amides which arecharacterized by solving the mixed fatty amides in a solvent to proeighteen-carbon chain length, some poly-unsaturated and other unsaturated to a lesser degree.

said method comprising synthesizing amides of eighteen-carbon chain length from the fatty bodies, dissolving said amides in solvent of greater polarity than a petroleum solvent, lowering the temperature of the solvent to precipitate the amides which are not polyunsaturated, separating such amides from the solution, separating the fatty amides remaining in solution from the solvent and hydrolyzing the said fatty amides to linoleic and linolenic acids.

LATIMER D. MYERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,042,729 Ralston June 2, 1936 2,113,960 Grote Apr. 12, 1938 2,285,795 Batchelder June 9, 1942 2,340,104 Brown Jan. 25, 1944 OTHER REFERENCES Falciola, Gazz. Chim. Ital. (1910) vol. 40, pages 217219 and 425-435. Pages 224-226 and 425 are relied upon. v

Ralston et 9.1.. Journal of Organic Chemistry,

vol. 7 (1942) pp, 546-555. I

Ralston et al., Journal of Organic Chemistry vol. 8 (1943) pp. 473-487. 

1. THE METHOD OF OBTAINING BATCHES OF MIXED FATTY ACIDS OF DIFFERENT MELTING POINTS, SAID METHOD COMPRISING PREPARING FATTY AMIDES, DISSOLVING THE FATTY AMIDES IN A SOLVENT, LOWERING THE TEMPERATURE OF THE SOLVENT TO PRECIPITATE PART OF THE FATTY AMIDES DISSOLVED, SEPARATING THE PRECIPITATED FATTY AMIDES FROM THE FATTY AMIDES REMAINING IN SOLUTION, SEPARATING THE FATTY AMIDES FROM THE SOLVENT, AND CONVERTING THE FATTY AMIDES INTO CORRESPONDING FATTY ACIDS. 